A=[1 1 1; 1 2 4; 1 3 9];
b=[6; 15; 28]
a=A\b
A*a

x=[1 2 3];
y=[6 15 28];
plot(x,y,'o');
hold on
t=0:0.01:4;
plot(t,a(1)+a(2)*t+a(3)*t.^2,'r')
xlabel('t')
ylabel('p(t)')
axis([0 4 0 30])